1. Field of the Invention
The present invention relates to a pyrolysis inlet system for use with a mass spectrometer.
2. Description of the Prior Art
In a mass spectrometer, ions of a sample are analysed based upon their mass or mass-to-charge ratio in order to determine the ions present and their relative proportions. It is therefore necessary in various forms of mass spectrometers to be able to introduce the molecules to be analysed into the evacuated interior of the apparatus without affecting the vacuum within the apparatus.
In the prior art, the introduction of pyrolysate into the mass spectrometer relies upon a trap with an entry which may be opened to atmospheric conditions to allow the sample to be entered and which is then closed to seal off the sample from the atmosphere. The trap is then evacuated by a purposely provided pump, and when the desired vacuum conditions are reached a valve is opened to connect the trap to the interior of the mass spectrometer.
When the sample is under vacuum conditions, it is pyrolysed and the pyrolysate passes through an expansion chamber and a capillary tube to form a molecular beam for ionisation and subsequent analysis in the mass spectrometer. The need for the expansion chamber stems from the fact that on pyrolysis the pressure within the trap increases substantially and a large volume expansion chamber is required to broaden the pressure pulse so that the molecules travelling down the capillary tube for analysis should do so at a controlled rate, the differential pressure being excessive in the absence of such an expansion chamber.
The prior art system as described above, requires a complicated arrangement of pumps and gates which is expensive and cumbersome to implement and the invention seeks to provide an inlet system which mitigates these disadvantages.